In radiographic imaging, a technique of energy subtraction is employed to select images of a soft part and images of a bony part. Subtraction images of a soft part or bony part can be outputted by acquiring high-voltage images and low-voltage images, and carrying out subtractions of these images. In recent years, a technique of carrying out energy subtraction in dynamic images has been proposed, in which radiation corresponding to a high voltage value and radiation corresponding to a low voltage value lower than that are emitted, as switched back and forth, to acquire high-voltage images and low-voltage images alternately, thereby acquiring subtraction images successively (see Patent Document 1, for example). In this technique of Patent Document 1, one of the high-voltage image and low-voltage image is acquired in the odd frames of (2m−1) frames, and the other of the high-voltage image and low-voltage image is acquired in even frames of 2m frames, to use an energy difference between the images in (2m−1) frames and 2m frames adjoining each other in time. And a subtraction process is carried out concerning the image in the (2m−1) frames and the image in the 2m frames.